1. Field of the Invention
The present invention is broadly concerned with an improved, low-cost process for the production of road deicers making use of water plant residuals typically containing calcium and magnesium compounds. More particularly, the invention pertains to such a method wherein the water plant residuals are initially concentrated and reacted with organic acids such as acetic acid to yield calcium acetate, calcium magnesium acetate (CMA) or a mixture of such acids such as acetic and propionic acids to give a calcium magnesium acetate/calcium magnesium propionate (CMA/CMP) deicer.
2. Description of the Prior Art
The importance of the effectiveness removal of snow and ice from roadways during winter can not be overemphasized in terms of reducing traffic accidents and fatalities. Approximately ten million metric tons of salts, principally sodium chloride and some calcium chloride, are used annually on roadways in the United States for this purpose. While these salts are inexpensive and effective deicers, there are numerous harmful effects attendant to their use. These include the accelerated corrosion of automobiles, degradation of structural and reinforcing steel, damage to roadside vegetation, and harm to drinking water supplies. Among the various alternative compounds heretofore proposed as substitute deicers, calcium magnesium acetate (CMA) has emerged as the leading candidate, based on its effectiveness in deicing and reducing corrosion rates and environmental effects. However, the cost of this product is approximately twenty times or more than that of rock salt. Therefore, the use of CMA by various local and state governmental agencies has been quite minimal owing to cost considerations.
U.S. Pat. No. 4,855,071 describes a slurry process for preparing CMA wherein alkaline earth or alkali metal carboxylates are formed and the slurry is heated and distributed as a thin layer on substrate particles. The basic raw materials suggested for such CMA production are dolomitic lime and glacial acetic acid. Similarly, U.S. Pat. No. 4,636,467 suggests use of dolomitic lime with acetic acid for the production of CMA.
A principal drawback to the widespread use of CMA and similar road deicers is the cost thereof. While dolomite is relatively inexpensive, the overall cost of synthetic road deicers could be substantially lowered if still less expensive starting materials could be employed.
It is known that residuals (sludge) from water softening plants contain calcium and magnesium salts as well as inorganic and organic impurities. The amount of precipitates such as ferric or aluminum hydroxide in the sludge can be virtually negligible if the plant has primary and secondary clarifiers and lime sludge is withdrawn from the primary basin. The amounts of inorganic constituents such as clay and organic compounds will depend on the raw water characteristics. In most cases, these amounts of impurities will be quite small for ground waters; for surface waters, these impurities may also be present only in small quantities if presedimentation basins are used. In most cases, therefore, the main constituents of water plant sludge from softening plants will be calcium carbonate, calcium hydroxide and magnesium oxide, although other impurities will almost always be present in greater or lesser amounts.
Of course, water plant sludges have almost no economic value and indeed can present a disposal problem in their own right. Therefore, any economically viable use of such sludges would represent a distinct breakthrough in the art.